The present invention relates generally to two-stroke engines and, more particularly, relates to a method and apparatus for starting a rope-start, two-stroke engine.
Rope-start, two-stroke engines are used in a variety of applications including outboard marine engines, snowmobiles, personal watercraft, snow blowers, and weed trimmers. These engines are started by manually actuating a starter mechanism that drives the engine to rotate. Engine rotation initiates a firing sequence by enabling the supply of electrical power to the engine's fuel injection and/or ignition systems at the next appropriate engine rotational position(s). The most common manually actuated starter mechanism includes a rope that is wound around a spool coupled to the engine's flywheel either directly or via one or more gears. The rope unwinds from the spool when it is pulled by the operator, thereby driving the spool and the flywheel to rotate.
Consumers demand that rope-start engines start with as little manual input as necessary. Many original equipment manufacturers demand that the engine must start on the first pull. However, starting an engine with one pull of the rope-start mechanism is hindered by several factors.
For instance, the rope-start mechanism imparts only a relatively small number of revolutions to the engine, limiting the number of available revolutions to initiate and successfully implement the engine's firing sequence. In a so-called “short-pull” engine, manual actuation of the rope-start mechanism drives the engine to rotate through no more than three-to-five revolutions. This small number of revolutions creates only a relatively small window of opportunity to initiate and successfully implement an engine firing sequence.
In addition, the engine must undergo at least part of a revolution before a firing sequence can be enabled. This limitation on engine starting stems from the fact that the absolute position of the engine must be determined before its firing sequence can be enabled. The engine's computer typically determines the engine's absolute rotational position by detecting spaced markers on a rotating component of the engine. These markers may include a plurality of equally-spaced “indicator” markers and a few additional, unequally-spaced “indexing” markers. The locations of and spacings between the markers are stored in a map or table of the computer's memory. The computer can determine the angle of rotation from a given point by counting the number of indicator markers from that point. The indexing markers form starting points and ending points for determining the engine's absolute position and direction of rotation upon engine start-up. At least two indexing markers must be detected to determine absolute engine rotational position. Specifically, upon detecting the first indexing marker, the computer resets its internal counter and begins to count the number of indicator markers between the first indexing marker and the second indexing marker. Then, upon detecting the second indexing marker, the computer can determine the angular spacing between the first and second indexing markers. The computer then compares the determined spacing to the table or map of known spacings. Based on this comparison, the computer can identify the indexing marker that is detected second and accordingly, the rotational position of the engine.
Quick engine starting is further hindered in a battery-less engine that relies on electricity generated by rotation of the engine to supply electrical power to the computer and other engine components, such as the engine's fuel injection system and/or ignition system. The typical engine must undergo at least part of a revolution, and sometimes a complete revolution or more, before generating enough power to operate the computer. This “power-up” requirement delays the computer's detection of the absolute engine rotational position and, therefore, further delays enablement of the firing sequence. All of these factors conspire to render it difficult to initiate a firing sequence in less than about one full engine revolution.
Another complicating factor that hinders quick-start and that is unique to two-stroke engines is the need to prevent engine counter-rotation. Counter-rotation occurs when the engine runs in reverse so that the crankshaft rotates in a direction opposite the intended direction. Because counter-rotation risks damage to the engine and possibly components powered by it, counter-rotation must be detected to prevent firing of the counter-rotating engine. In a system in which the engine's position is determined by detecting and identifying two indexing markers on a rotating component of the engine, counter-rotation is detected by detecting and identifying a third indexing marker disposed at an angle β from the second indexing marker that is different from the angle α separating the first and second indexing markers. The engine's rotational direction can then be determined by determining the sequence in which the second and third indexing markers are detected.
Unfortunately, the need to detect and identify a third indexing marker additionally delays enablement of an engine's firing sequence and further hinders quick-start. In a short-pull engine, this additional delay in firing sequence enablement may mean the difference between a successful first pull start and an unsuccessful first pull start.
The need therefore has arisen to provide a method for quick starting a rope-start, two-cycle engine that does not require the direction of rotation of the engine to be sensed before enabling a firing sequence.